1. Field of the Invention
The present invention relates to a control apparatus, a storage apparatus, and a head control method that detect a read error of servo information (position information) on a storage medium.
2. Description of the Related Art
A servo frame is written between sectors on a general magnetic disk. The servo frame includes servo information such as rough position information in the disk radial direction, detailed position information in the disk radial direction, and a correction value (postcode) of position information in the disk radial direction. A checksum is included in the postcode in order to prevent a read error of the postcode. Only when a checksum that has been read out from a recording medium is determined to be correct, a correction value that has been read out can be used.
For example, as a prior art relating to the present invention, a magnetic disk apparatus and its manufacturing method that correct non-flatness of a position signal after servo-writing to prevent a track pitch variation are available (refer to, e.g., Patent Document 1: Japanese Patent No. 3336819).
However, there may be a case where a checksum is determined to be correct even when a correction value has improperly been read out. If the improper correction value is used, control processing according to erroneous position information is performed and, in the worst case, data to be written in a given track is written in the area so close to an adjacent track with the result that data in the adjacent track cannot be read out.
If correction values are stored in an ROM (Read Only Memory) or the like, it is possible to avoid the above problem. However, this configuration requires a corresponding memory capacity, resulting in an increase in cost. Thus, it is not possible to completely avoid the erroneous detection of a checksum as long as the correction values are stored in a recording medium.